Alternative refrigerants such as HFC-125 (C2HF5) and HFC-32 (CH2F2) have been widely used as important replacements for CFC, HCFC, etc., which cause ozone layer depletion. However, these alternative refrigerants are potent global warming substances, thus creating concern that diffusion of the refrigerants would increase global warming. As a preventive measure, these refrigerants are recovered after use. However, complete recovery of the refrigerants is impossible. In addition, the diffusion of these refrigerants due to leakage, etc., cannot be ignored. The use of CO2 or hydrocarbon-based substances as alternative refrigerants has also been investigated. However, because CO2 refrigerants have low efficiency and devices using such refrigerants inevitably become large, CO2 refrigerants have many problems in terms of the overall reduction of greenhouse gas emissions, including energy to be consumed. Furthermore, hydrocarbon-based substances pose safety problems due to their high flammability.
2,3,3,3-tetrafluoropropene (HFO-1234yf, CF3CF═CH2), which is an olefinic HFC having a low global warming potential, has recently been attracting attention as a material to solve the above problems. HFO-1234yf, used alone or in combination with other substances, such as hydrofluorocarbons, hydrofluoroolefins, and hydrochlorofluoroolefins, is expected to be useful as a refrigerant, and additionally as a blowing agent, propellant, extinguishing agent, or the like.
Some processes for producing HFO-1234yf have been disclosed. In most of these processes, a hydrohalopropane such as a hydrochloropropane or a hydrohalopropene such as a hydrochloropropene, used as a starting material, is fluorinated with hydrogen fluoride to ultimately prepare HFO-1234yf.
For example, Patent Literature 1 listed below discloses a process in which HFO-1234yf is produced, via a hydrochlorofluoroalkane or a hydrochlorofluoroalkene, by subjecting a haloalkane or a haloalkene as a starting material to fluorination with HF, dehydrochlorination, etc.
Patent Literature 2 listed below discloses a process in which HFO-1234yf is produced, via a hydrochlorofluoroalkane, hydrochlorofluoroalkene, etc., by subjecting a hydrochloropropane, hydrochlorofluoropropane, etc., as a starting material to fluorination with HF in the presence of a catalyst.
Furthermore, Patent Literature 3 listed below discloses an integration process for preparing HFO-1234yf by using 1,1,1,2,3-pentachloropropane (HCC-240db) as a starting material, fluorinating the starting material with HF to produce HCFO-1233xf, and then adding HF to the thus-obtained HCFO-1233xf to produce HCFC-244bb, followed by dehydrochlorination.
All of these processes use a hydrochlorocarbon as a starting material to prepare HFO-1234yf by a multiple-stage reaction process. However, each of the processes has a problem of a cost increase due to the use of a catalyst and also has a drawback of insufficient selectivity resulting from the formation of many products other than the desired product, i.e., HFO-1234yf. Further, the use of higher chlorinate as a starting material poses another problem in that catalyst activity is likely to deteriorate as reaction progresses.